Optical variable devices (OVDs) are often used as anti-counterfeit means. OVDs include holograms, diffraction gratings, multilayer films, and the like. OVDs, using light interference, display a stereo image or a decorative image which produces a color change depending on the observation angle. In addition to such visual effects, advanced technology is required for manufacturing OVDs. Accordingly, OVDs are used as display bodies for preventing counterfeiting of credit cards, securities, certificates, notes, tickets, or the like. Additionally, OVDs have recently been used as authentication labels to prove authenticity of a genuine product, or for a sealing label to seal the packaging of a product.
However, the widespread use of OVDs have resulted in distribution of counterfeit products having a visual effect similar to that of genuine OVDs.
Recently, a latent image device applied with polarized technology has been proposed. The proposed latent image device visualizes a latent image by observation through a polarizing film and enables authentication. However, to determine authenticity of the latent image device, a dedicated verifier such as a polarizing film, is required. Generally, retailers and service providers provide dedicated verifiers for authentication corresponding to the latent image device received from a consumer to determine the authenticity of the device. However, hardly any information as to whether a latent image device has been used is available to average consumers. Accordingly, it is difficult for the average consumers to acquire in advance the verifiers corresponding to those latent image devices which would be acquired in various circumstances.
As to this problem, JP 2001-63300 A proposes an anti-counterfeiting medium provided with both an OVD enabling authentication to some extent by average consumers, and a latent image device enabling authentication by retailers and service providers (see PTL 1). The latent image device in this proposal includes a latent image portion and a non-latent image portion. The latent image portion, which is optically anisotropic, does not form a latent image when observed under ordinary light (unpolarized light), but forms a latent image when observed under polarized light. The non-latent image portion, which is optically isotropic, does not form any image when observed under ordinary light or polarized light.